1. Field of Invention
This invention relates to gravity-driven car racing, specifically an improved track based on a controlled-friction design for use in racing such as the popular Pinewood Derby race.
2. Prior Art
Millions of Pinewood Derby races have been run since the inception of the race in 1953, mostly by Cub Scouts and their parents. But the currently available race tracks have a problem in that friction between the car wheels and the track is not controlled. Refer to the prior art FIGS. 1 and 2 which point out views typical of ramps currently in use that do not control friction. In one commonly used ramp in FIG. 1, the ramp material used to form either one lane or several side-by-side lanes has uncontrolled regions where the level of friction between the track and the wheels of a gravity-driven car limit the potential performance of the car. In some areas friction between the race car's wheels and the track should be increased and in other areas it should be decreased. Careful examination of a car during racing shows the following prior art problem areas:    1) In a race car's guiding process, the car wheels must straddle the center guide strip from start to finish. The friction level between the wheel and the smooth flat surface of the wheel rolling channel is too low allowing traction loss and undesirable side-to-side cross-track movement of a car. This causes bumping against the center guide strip, here formed from 2 guide rails, resulting in a loss of energy and car speed. Moreover, the distance a car must travel to reach the finish line increases as guide strip bumping increases, also resulting in a slower race time.    2) During the guiding process there is too much friction from the inside of the car wheels rubbing against the center guide strip which causes loss of speed even in the absence of direct bumping.    3) There is an adhesive force between a car wheel's flat tread and the flat track surface, commonly called rolling friction, which also results in a loss of car speed.
Refer now to FIG. 1 Prior Art where a lane section 10 has connecting pins such as 14 for end-to-end joining with other sections and also a tongue 11 and groove 12 for side-by-side lane joining. The lane has flat wheel rolling channels such as 15 for the wheels and a central guide strip as shown here formed by a pair of raised guide rails such as 13. Extruded aluminum or plastic are commonly used materials for the prior art tracks.
In FIG. 2 there is shown an end-view, from the front, outline of a car body 16 on the prior art track of FIG. 1. More detail on the problems caused by the above three friction areas are:
a) In FIG. 2 we see where prior art tracks can have a low friction that exists in the area 23 where the wheel smooth bottom surface contacts the smooth flat rolling channel surface 18. This low friction allows a force, such as those commonly encountered during racing dynamics, to increase the motion 25 when traction is lost. This can result in a substantial impact when the wheel inside 22 bumps against the guide rail 21 as explained in 1) above. The same effect applies to the motion 24 and impact between surfaces 19 and 20 on the car's passenger side. In addition to the energy loss and car forward speed reduction from the central guide strip bumping, the sideways motion itself detracts from a straight path and increases the time to the finish line.
b) Again, in FIG. 2, the movement 25 of the body and an attached car wheel 17 can be more gradual. This movement causes the inside of the wheel, 22, to rub against the outside, 21, of the guide rail 13. The wheel is a plastic material, usually polystyrene, which can develop considerable rubbing force from this sliding friction with the guide rail which slows down the speed of the car. Similarly, movement 24 of the body and attached car wheel on the passenger-side of the car causes the inside surface of this wheel, 19, to rub against the outside, 20, of the guide rail on the passenger side. Sometimes a car will alternate sides when contacting the guide rail with its wheels on its way to the finish line. At other times, depending on the wheel alignment, it is possible for wheels on only one side of the car to rub the guide rail for a substantial part of the distance from start to the finish.
c) The wheel “foot print” is a relatively large contact area between the flat and smooth wheel tread surface 23 and the smooth rolling surface 18 which contributes to an adhesive force between these surfaces that requires energy to separate. This adhesive force operates perpendicular to the wheel channel rolling surface whereas the sliding friction in 1) and 2) above is a tangential force opposite to the direction of motion. This adhesive force, sometimes known as rolling friction, is unlike sliding friction in that it does depend on the contact area 23.